Telecommunications carriers typically deploy optical fibers for transmitting optical signals from one point to another. Polarization mode dispersion (PMD) is a form of modal dispersion where two different polarizations of light in an optical fiber, which normally travel at the same speed, travel at different speeds due to random imperfections and asymmetries in the optical fiber. PMD causes random spreading of optical pulses, and creates problems for optical signals transmitted over the optical fiber. Unless compensated for, PMD ultimately limits the rate at which data can be transmitted over the optical fiber.
PMD splits an optical signal in the time domain along two polarization modes. PMD is an average value of a number of differential group delays (DGDs) observed when measuring an optical signal. DGD is a time separation or delay provided between the two polarization modes of the optical signal, and may be measured at an optical receiver. DGD is an instantaneous event and varies randomly with wavelength and time.
For a dense wavelength division multiplexing (DWDM) channel operating at a wavelength, the DGD changes with time. An optical channel may not experience degradation for a specified DGD value. For example, a ten (10) gigabits per second (G/s) data rate channel may be specified for a DGD value of thirty (30) picoseconds (ps). This means that the ten G/s channel may fail when the DGD value is more than thirty picoseconds. A DGD value greater than thirty picoseconds may occur, but may occur very infrequently (e.g., may occur less than 0.01% of the time). During less than 0.01% of the time, the ten G/s channel may not operate. Current systems are unable to eliminate or reduce channel inoperability for such a time period, and are unable to make the channel more tolerant of PMD for such a time period.